Steel-Plated Glulam Beam? 1

[mmalloy]

I have a residential client with a 5-1/8" x 15" GLB, 38 ft long, and continuous across two posts. The posts are evenly spaced at 1/3 and 2/3 of the beam's length. A load analysis shows that as currently constructed, the beam is properly sized for the calculated shear and moments.

The owner wishes to remove one of the posts to create more uninterrupted space in the living room. When the loads are calculated under this scenario, the beam is overstressed in bending both in the middle of the new, longer clear span and in negative bending where it passes over the remaining support post.

I am considering reinforcing the tension faces of the beam with steel plates to increase the bending capacity, but can not find an established methodology for analyzing such a built-up beam. Does anybody know of a recognized method for analyzing a steel-reinforced glulam beam? Any advice would be much appreciated.

- Mike Malloy, PE

 

[UcfSE]

Have you tried the method of transformed sections?

 

[DVSVojvoda]

Mike,
Trying to develop forces into a Glulam, or any steel to wood connection for that matter is:

1. Aesthetically unpleasant
2. Not economical.

UcfSE is correct about converting the geometrical properties as a function of its elasticity, however, most W12's and W14's are designed/sized heavier at 30'-0" for deflection and not bending stress. So I think deflection would be a greater hurdle than that of capacity. (Been down that road many a time)

 

[JAE]

Don't forget that when you take the column out, the remaining supports receive the additional load and may not have the required capacity. This includes the connections of beam to column/wall and the foundation or structure below that supports them.

In other words, follow the load path through the whole system.

 

[samdamon]

Design method for steel flitches on wood members can be found in Chapter 13 of "Structural Design in Wood" by Stalnaker and Harris. When designing the strengthening keep in mind that the amount of weight one or two guys can lift into place at the ridge at one time is limited.

Since your ridge is existing, you probably don't have easy access to the sides or top of the ridge member. It might be simpler to build a gable shaped frame to replace the post, or to add an additional member beneath the existing ridge (if headroom allows), rather than strengthen the existing ridge section.

I second JAE's coments about load path. Be careful about increasing the forces on other portions of the structure besides the ridge. Good luck.

 

[boo1]

You MUST ensure that any flitch beam is provided with adequate bearing, fastening methods, and lateral restraint or lateral stability.

See Flitch examples at:
<

http://www.destefanoassociates.com/tech/flitch.pdf>

Flitch Plate and Steel I-Beams <

http://www.toolbase.org/Docs/MainNa...pdf?TrackID=&CategoryID=1153&DocumentID=2947>

Why not just replace the GLB with a steel beam?

 

[apetr26542]

I observed a reinforced glulam beam in a classroom, the beam had side plates and was connected via through bolts. The through bolts started to cause delamination in the plies as the bolt was located between plies.

 

[RARWOOD]

When you are checking the glulam for tension on the top I am assuming you are use the values from the 2001 N.D.S. or the 2005 edition. Based on new research the allowable stress for tension on the top of a glulam due to bending, has been increased over the values shown in the 1997 N.D.S.

I have seen cases where additional laminations have been added to the underside of a glulam in the field. In your case that may not be very practical for several reasons. First of all you may not have the head room to increase the beam depth.

Second of all the cost may be too high as very tight quality control is required and it requires a contractor with the experience to do the job properly.

Among the difficulties faced in the field, is applying enough clamping force to the laminations to assure a proper glue bond is achieved. Also you must have in place procedures to assure your glue is properly mixed, applied and cured.

Another approach might be to add a full length steel plate to the underside of the glulam beam to carry the tension. You then could rout out a laminations and then attach it as a cover over the steel plate.

What ever you do I would be conservative. All the advice given by others above is good advice and should be considered in developing your solution.

 

[kxa]

Can you replace the column/post with a truss that can span from wall to wall? If so, you would need to place two posts in the walls.